For focusing mechanism of three-line stereo mapping CCD camera, the special techniques are required to ensure imaging in focus and keep the position accuracy of the inner orientation elements unchangeably. In order to implement refocusing the camera in-orbit, focusing mechanism must have high position precision and movement accuracy. Two principles of adjustment mechanism are presented. One is drove by screw, guided by two rails;the other adopted the tube cam mechanism to transfer the cam’s rotation into the CCD’s movement along optical axis. The whole focusing system of cam focusing method is realized in compact volume and high stability. Experiment results indicate that focusing precision is less than ±11μm, rotation error less than 5″, and linearity error less than 8″.